Empty pdf file - view only

Hi,
Nextcloud Hub 8 - (https://hetzner.com) (29.0.5)
Pdf Viewer (2.10.0)

The pdf viewer pops up an empty file for user with a view-only mode.
As soon a user can-edit, the file shows up correcty.
Somethings wrong here but I have no clue how to set it up.
Need help